Oscillation generation system



Patented May 2, 1939 angers PATENT OE'EIQE OSCILLATION GENERATION SYSTEM Nils E. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 19, 1935, Serial No. 7,160

10 Claims.

This invention relates to a method of and apparatus for generating high frequency oscillations.

An object of the present invention is to provide an apparatus for the generation of high frequency oscillations which is of light weight and can be used in aircraft.

Another object is to provide a highly efficient and simple oscillator circuit requiring as few adjustments as possible.

The foregoing objects, and others are achieved in accordance with the invention by providing a push-pull type of oscillator circuit which dispenses with the need for rectifier tube equipment and which has only a single tuning element.

More specifically, the preferred embodiment of the invention comprises a tube having within a single envelope a pair of interconnected plates disposed on opposite sides of a common grid, with a filament individual to each plate for causing the latter to emit electrons. Only a single tuning element is required, and this is provided in the plate circuit in the form of a trombone or telescopic slide. The grid has no tuned circuit.

An advantage of the present invention is that the common grid is always in a neutral condition whereby it will not pick up stray radio frequency oscillations.

A further advantage is that there is required for the practice of the invention only alternating current energy for energizing the filaments and for applying desired polarizing potentials to the electrodes of the oscillator.

Other objects and advantages will appear in the subsequent detailed description whichis accompanied by a single drawing illustrating a transmittercircuit embodying the principles of the invention.

Referring to the drawing, there is shown an oscillator circuit comprising within a single envelope E, a pair of plates P1, P2 which are oppositely arranged with respect to a centrally located common grid G, and a pair of filaments F1, F2 whose purpose is to provide heating of the plates P1, P2 by electron bombardment. In order to prevent detrimental capacity coupling between the filaments F1, F2 and plates P1, P2, the filaments are not mounted too close to the plates.

Plates P1, P2 are connected together by means of a tunable trombone slide S, the center point of which is connected to ground and to one plate of a condenser C, the other plate of which is-coupled to the midpoint 3 of the secondary winding of a transformer T3 and to the grid G. It is preferred to coat the inner surfaces of the plates P1, P2 with electron emissive material, otherwise the plates will have to be heated to high temperatures to emit electrons.

Filaments F1 and F2 are heated by alternating current through transformers T1 and T2 respectively, and the midpoints of the secondary wind ings of these transformers are respectively connected to opposite terminals I, 2 of the secondary winding of transformer T3. The primary winding of transformer T3 is also supplied with alternating energy which, if desired, may emanate from the same source as that supplying heating current for the filaments.

Coupled to the trombone slide S through a pair of wires This a radio frequency utilization circuit herein shown by way of example, as an antenna A. It will be noted that there is zero direct current potential on the plates P1, P2.

In operation, the centrally located grid G is always maintained at a positive potential relative to the filaments F1, F2 and the plates P1, P2. This will be apparent from the fact that when either terminal l or 2 of the secondary winding of transformer T3 is negative, due to the alternating current energy applied to the primary winding of T3, electrons will pass from the filaments to the plates. Thus the filament systems F1 T1 T3 T2 F2 will be at a positive potential. Since the potentials of terminals l and 2 continuously alternate, midpoint 3, which is directly connected to grid G, is always positive with respect to that filament which at the moment is passing electrons to its associated plate. It may be said that the heating circuit of the two filaments is thus used as a full wave rectifier for obtaining the potential for the grid. It will thus be observed that the filaments F1, F2, which have a floating positive direct current potential, must swing negative when passing electrons to their plates.

When the electrons which pass from the filaments F1 and F2 land on the plates P1 and P2 heat is produced from the resulting bombardment. Since these plates are coated on the sides facing the grid with a substance which emits electrons at moderate temperatures, electrons will fiow toward the grid G, which is maintained at positive potential by virtue of its connection to the filament system. As the electrons travel toward the grid they are accelerated, and a number of the electrons will collide with the grid. Such electrons have very little usefulness since they collide with the grid at their maximum velocity, and the kinetic energy thus possessed by them when colliding is lost in the form ofheat,

light and X-rays, although the latter are only observed at very high bombarding velocities.

The electrons which do not land on the grid but instead pass through the grid mesh are immediately subjected to a retarding force and will, in most cases, lose all their velocity before reaching the opposite plate. The electrons will thus come to a standstill in front of the plates and tend to retrace their path. Such a slowing up of the velocity represents a condition similar to a trafiic congestion on a highway at points of low tramc speed. The accumulated electrons, since they are electric charges, will alter the electric field in the interelectrode space in such a way that later arriving electrons are made to retrace their path sooner. The arrival of these later electrons also tends to hold over those that arrived earlier. In this way it can be seen that the random electrons are organized into a group having a group motion, and it is this organized group oscillating back and forth, which is believed to do work on the external circuit. The period of such oscillations depends, of course, on the direct current voltages employed. The external circuit tuning is therefore arranged to correspond to the voltage conditions in the inter-electrode space and the dimensions of this space. These oscillations, which are at radio frequency, are utilized by antenna A which is inductively coupled to trombone S through lines TL.

The best available theory indicates that the work performed by the electron before it lands is most useful. Since an electron is a negative charge, and a charged body in the presence of a metallic conductor (in this case the entire electrode circuit system) produces, by electrostatic induction, images of opposite polarity, so-called bound charges are caused to appear in the conductor. When the charge (electron) in the space, in the neighborhood of this conductor, moves, the bound charges in the conductor move in the same manner as an image moves when the subject moves. These motions of the images, as the electrons move, represent electric currents. Thus, in any vacuum tube phenomena, the electrons are believed to do their useful work while passing through the inter-electrode space. When these electrons strike an electrode, they neutralize the image that comes to meet them, and thus induce no more current in the external system. The energy they possess at landing is lost in the forms already referred to. It is therefore believed important that the electron motion be loaded as much as possible so that the kinetic energy given to the electrons by the direct current potentials on the tube elements will be transformed as much as possible into induced currents in the external circuit before they land. The remaining energy represented by electrons when they land should be a minimum.

Although the foregoing theoretical explanation is believed to be correct and has been given in order that the operation of the invention may be better appreciated, it is not of necessity complete, nor does the operation of the invention depend upon its accuracy or otherwise.

The oscillations thus produced may, if desired, be modulated in accordance with the message waves to be transmitted. This is accomplished in one suitable way, known as the l-leising scheme, by inserting a choke coil in the grid lead and supplying the signals to the input circuit of a modulator tube M whose anode is in circuit with the grid G, as shown.

It is to be understood, of course, that the invention is not limited to the precise arrangement of parts shown, since it is possible, among other things, to dispense with the plates P1, P2 and utilize the filaments themselves as the plate elements. The use of plates is preferred, however, bcause there are thus obtained uniform emission surfaces without internal voltage drops, and it is possible to use tube E as a rectifier; at the same time there is obviated the clifficulty of standing waves on the filament wires.

It is also to be understood that the term ground used in the specification and claims is intended to define any point or surface of zero or relatively fixed radio frequency potential, since in practice connections in high frequency systems actually rarely extend to earth.

What is claimed is:

1. An oscillation generation system comprising within a single envelope a pair of spaced plates having their inner surfaces coated with an electron emissive material, a filament individual to each plate for heating same, a grid located between said plates, an external, adjustable, U- shaped conductor connecting said plates together, a first transformer having its primary connected to a source of alternating energy and its secondary connected to the legs of one of said filaments for heating same, a second transformer similarly connected to said other filament, a third transformer having its primary winding also connected to a source of alternating energy but the respective terminals of its secondary Winding connected to the midpoints of the secondary windings of said first and second transformers, a conductive connection from the midpoint of the secondary winding of said third transformer to said grid, and a capacitive coupling between. said last connection and the center of said U-shaped conductor, a connection from the center of said U-shaped conductor to ground, and an antenna inductively coupled to said U-shaped conductor.

2. A system in accordance with claim 1, including means in circuit with the grid for modulating the oscillations produced.

3. A system in accordance with claim 1, including a choke coil in the conductive connection between said grid and the midpoint of the secondary winding of said third transformer, and an electron discharge device having an input circuit coupled to a source of signal waves and an output circuit coupled to the junction of said grid and choke coil.

4. An oscillation generation system comprising, within a single envelope, a pair of spaced plates having their inner surfaces coated with an electron emissive material, a filament individual to and facing the outer surface of each plate for heating same, a grid located between said plates, an external, adjustable, U-shaped connection between said plates, a condenser having a pair of armatures one of which is directly connected to the center of said U-shaped connection, individual conductive paths from the other armature of said condenser to said grid and said filaments, and a utilization circuit coupled to said U-shaped connection.

5. An electron discharge device system comprising within an envelope, a grid, a source of electrons, and a plate located between said grid and source of electrons, said plate having its surface nearest said grid coated with material of greater electron emissivity than the opposite surface nearest said source, a connection from said plate to ground, and. means for heating said source, whereby electronic bombardment of said plate from said source causes electron emission from the surface of said plate nearest said grid, and means for alternately changing the relative polarity of said grid from a positive potential to a negative potential with respect to said source, and for maintaining said grid always positive relative to ground.

6. An electron discharge device system comprising within an envelope, a grid, a source of electrons, and a plate located between said grid and source of electrons, said plate having its surface nearest said grid coated with material of greater electron emissivity than the opposite surface nearest said source, and means for heating said source, whereby electronic bombardment of said plate from said source causes electron emission from the surface of said plate nearest said grid, a similar arrangement of another plate and another source of electrons on the other side of said grid oppositely disposed with respect to said first plate and first source, an alternating voltage to be rectified coupled between said two sources, and means including a filter for maintaining said grid at a potential which is substantialy unvarying at the frequency of the rectified voltage.

'7. An oscillation generator comprising a fullwave rectifier having a pair of filaments, each of which has individual thereto a plane anode located between said filaments, a tuned circuit coupled between said anodes, the surfaces of said anodes removed from their respective filaments being coated with an electron emissive material, an electrode located between said anodes, and means for periodically changing, alternately, at an audio frequency rate, the relative polarities of said filaments relative to said electrode, whereby said electron emissive surfaces function as the cathodes of said oscillation generator and produce oscillations in said tuned circuit.

8. An oscillation generator comprising a rectifier having .a filament and a plane anode, the surface of said anode removed from said filament being coated with an electron emissive material, an electrode separated solely by ethereal space from said emissive surface of said anode, a tuned circuit coupled to said anode and to ground, and means for causing said electrode to assume, alternately, positive and negative potentials relative to said filament, whereby oscillations are produced in said tuned circuit and said electron emissive surface functions as the cathode of said oscillation generator.

9. An oscillation generator in accordance with claim 8, characterized in this that said filament is thermionic.

10. An oscillation generator comprising a pair of electron emissive surfaces, a perforate electrode between said surfaces, a heating filament located on the side of each of said surfaces away from said perforate electrode, means for maintaining said emissive surfaces at zero direct current potential and said perforate electrode at a positive direct current potential and for causing said filaments to assume alternately positive and negative direct current potentials and a tuned circuit 'coupled between said surfaces.

NlLS E. LINDENBLAD. 

